If a user loses internet connection during a course, what happens?

It really depends on how it happens...if the outrage is not a critical point in the course, they may be able to continue without even knowing they lost connection...Many times it’s only realized when the course doesn't mark as completed but that is not always the case...also may depend on the content type, SCORM package vs. Docebo exam for example.

This was for a SCORM package within a course, so I’m thinking the user lost connection while going through the package and did not realize it. Their score was not recorded, though they provided a screenshot that showed they passed the quiz. 

Is there any warning message that pops up in Docebo if a user loses their internet connection while they are in the middle of a SCORM package? Our previous LMS had this feature. 

have never seen any message pop up in my tests...

I have not seen this happen when the internet goes out, but this does happen if there is a session time out set up on your platform.  If the user reaches a session time out while a SCORM is launched (like they walk away or check emails or do other things while their SCORM is open) and then they return to the course, they can successfully complete the SCORM.  But because the system times their session out, they are technically logged out of Docebo, so the completion is not recorded. 

You might want to check that Session lifetime setting in your platform to see if it is turned on.  It’s under the Advanced settings: 

If this is what the issue turned out to be, unfortunately, there is no message that will pop up warning the user of the session lifetime timeout.  They find out the hard way when trying to complete the SCORM.